Voltage dividers for high voltage gasfilled rectifiers



Dec- 1961 c. DILLON ETAL 3,014,157

VOLTAGE DIVIDERS FOR HIGH VOLTAGE GAS-FILLED RECTIFIERS Filed May 23,1960 Ch r/Es PI QXEI uNMr EN STIDM fa M Mg;

3,014,157 VOLTAGE DEBS FDR HiGH VOLTAGE GA= FELLED RECTlFiERS CharlesDillon, Cork, Ireland, and Gannar Engstrdm,

Ludvika, Sweden, assignors to Allmiinnasvenslra EiektriskaAirtiebolaget, Vasteras, Sweden, a Swedish corporation Filed May 23,196i Ser. No. 31,606 Claims priority, application Sweden May 26, 1959 2Qlaims. (Cl. 315-233) The present invention relates to a voltage dividerfor the intermediate electrodes in an anode unit in a high voltagegas-filled rectifier.

It is already known to connect the intermediate electrodes of an anodeunit in a high voltage gas-filled rectifier to a voltage dividercomprising a chain of the capacitors and resistors connected in seriesand inserted between the anode and the cathode of the gas-filledrectifier. It is observed that in voltage dividers of the known art,disturbances may arise during the ignition of the rectifier. it has beenvery difiicult to establish the cause of these disturbances but theprimary cause seems to be that it takes a certain time for the arc toextend from the cathode via the intermediate electrodes to the anode.

As the arc extends from the cathode and reaches the intermediateelectrodes, the capacitors betweensaid inter,- mediate electrodes andthe cathode of the rectifier will discharge through the arc. extensionof the are from the cathode to the anode takes a certain, even if it isa very short time, the discharge time will be longer for the capacitorsnearest to the oathode so that these capacitors are more discharged thanthe capacitors nearer to the anode. If a sudden change in the voltage ofthe anode of the rectifier arises before the arc has reached the anode,by way of example, because a parallel operating rectifier has ignited,so that the voltage between the anode and the cathode is shortcircuited,this voltage jump is absorbed by the resistors in thecapacitor-resistance chain in proportion to their resistances. Asexternal voltages of different frequencies coming from outside therectifier ought to be distributed during normal operation as equally aspossible between the intermediate electrodes, the resistors of the knownvoltage dividers are equally distributed in the capacitorresistor chain.A voltage jump arising at the ignition of the rectifier will thus beequally distributed between the intermediate electrodes. As thecapacitors, however, as mentioned above, are at this time unequallydischarged and thus have unequal voltages the consequence is that thevoltage distribution between the difierent intermediate electrodes issuch that for certain adjacent intermediate electrodes, the electrodenearer the anode will have a more negative potential than the electrodenearer to the cathode, which gives a disturbance at the ignition of therectifier. The ignition time is thereby extended and the currentdistribution between parallel operating anodes is rendered considerablymore difiicult and possibly quite spoiled.

These drawbacks are avoided by the present invention, which ischaracterised in that the resistors are unequally distributed along thecapacitor-resistor chain of the voltage divider so that the part of thischain nearer to the anode of the rectifier has greater resistance thanthe part nearest to the cathode. Consequent to this the greater part ofa voltage jump in the anode voltage will be distributed between theintermediate electrodes nearest to the anode and the smaller part of thevoltage jump between the electrodes nearest to the cathode. With asuitable distribution of the resistances in the resistor-capacitorchain, it is possible in this way to obtain a suitable distribution ofthe potential between the intermediate Owing to the fact that the3,014,157 Patented Dec lg, 1951 electrodes so that no disturbances inthe ignition of the I tion from the desired equal distribution ofexternal voltage during normal operation is thereby limited.

The invention will be further explained in the following with referenceto the accompanying drawing showing a form of the invention.

In the drawing is shown a gas-filled rectifier 1 with an anode 2, acathode 3 and a number of intermediate electrodes 4. A voltage divideris connected between the anode and the cathode and consists of acapacitor-resistor chain 5 in parallel with a purely resistive resistorchain 6. The capacitor-resistor chain 5 consists of a number ofcapacitors 7 and resistors 8, 9, 10, 11. The resistorcapacitor chain 5and the resistor chain 6 are parallel connected and have a number oftransverse connections, and the resistor chain 6 is connected to theintermediate electrodes 4 via series resistors 12. The main purpose ofthe resistor chain 6 is to give series resistances in the connections tothe intermediate electrodes 4 and to reduce the number of requiredcapacitors 7 in the capacitoresistor chain. When an arc extends from thecathode 3 towards the anode 2 the capacitors 7 of the capacitorresistorchain 5 between the cathode and the intermediate electrodes reached bythe arc will discharge in relation to the extension of thearc. When thearc has reached the intermediate electrodes 4 nearest to the anode, thecapacitors nearest to the cathode are discharged more than thecapacitors near to the anode and have thus a lower voltage than saidlast mentioned capacitors. If now a sudden decrease in the anode voltagearises, by way of example, caused by the ignition of a paralleloperating rectifier, this voltage reduction in the first moment will bedistributed on the resistors 8, 9, It) and 11 in the capacitorresistorchain. According to the invention these resistors are unequally great sothat the resistor 8 is the greatest and the resistor 11 the smallest. Asthe voltage jump is distributed between the resistors in relation to theresistances a greater part of the voltage jump is absorbed by theresistor 5, a smaller part by the resistor 9 and a still smaller part bythe resistor 10 and the smallest part by the resistor 11. Owing to thisthe differences of the voltage of the capacitors 7 caused because thecapacitors nearest to the cathode are more discharged than thecapacitors nearest to the anode, are compensated so that a suitabledistribution of the potential on the intermediate electrodes 5 isreached in spite of the voltage jump occurring, and the ignition can becarried out without disturbances.

We claim:

1. Voltage divider for an anode unit for a high voltage gas-filledrectifier; said anode unit provided with a number of intermediateelectrodes, said intermediate electrodes connected to said voltagedivider; said voltage divider comprising resistors and capacitors; saidresistors and capacitors connected in series between the anode and thecathode of the rectifier; the resistances of said resistors beingunequally distributed along the voltage divider in such a way that thepart of the voltage divider nearest to the anode has greater resistancethan the part nearest to the cathode.

2. An arrangement as set forth in claim 1, said resistors being voltagedependent resistors.

References Cited in thefile of this patent UNITED STATES PATENTS

